Gas separation is useful in many industries and can typically be accomplished by flowing a mixture of gases over an adsorbent material that preferentially adsorbs one or more gas components while not adsorbing one or more other gas components. The non-adsorbed components are recovered as a separate product.
One particular type of gas separation technology is swing adsorption, such as temperature swing adsorption (TSA), pressure swing adsorption (PSA), partial pressure swing adsorption (PPSA), rapid cycle temperature swing adsorption (RCTSA), rapid cycle pressure swing adsorption (RCPSA), rapid cycle partial pressure swing adsorption (RCPPSA), and not limited to but also combinations of the fore mentioned processes, such as pressure and temperature swing adsorption. As an example, PSA processes rely on the phenomenon of gas components being more readily adsorbed within the pore structure or free volume of an adsorbent material when the gas components are under pressure. In particular, the higher the gas pressure, the greater the amount of readily-adsorbed gas adsorbed. When the pressure is reduced, the adsorbed component is released, or desorbed from the adsorbent material.
The swing adsorption processes (e.g., PSA and/or TSA) may be used to separate gas components of a gas mixture because different gas components tend to fill the micropore of the adsorbent material to different extents. For example, if a gas mixture, such as natural gas, is passed under pressure through an adsorbent bed unit or vessel containing an adsorbent material that is more selective towards carbon dioxide than it is for methane, at least a portion of the carbon dioxide is selectively adsorbed by the adsorbent material, and the stream exiting the vessel is enriched in methane. When the adsorbent material on the adsorbent bed reaches the end of its capacity to adsorb carbon dioxide, it is regenerated by reducing the pressure, thereby releasing the adsorbed carbon dioxide. Then, the adsorbent material is typically purged and repressurized prior to starting another adsorption cycle.
The swing adsorption processes typically involve adsorbent bed units, which include adsorbent beds disposed within a housing and configured to maintain fluids at various pressures for different steps in a cycle within the unit. These adsorbent bed units utilize different packing material in the bed structures. For example, the adsorbent bed units utilize checker brick, pebble beds or other available packing. As an enhancement, some adsorbent bed units may utilize engineered packing within the bed structure. The engineered packing may include a material provided in a specific configuration, such as a honeycomb, ceramic forms, structured beds or the like.
Further, various adsorbent bed units may be coupled together with conduits and valves to manage the flow of fluids through the cycle. Orchestrating these adsorbent bed units involves coordinating the steps in the cycle for each of the adsorbent bed units with other adsorbent bed units in the system. A complete cycle can vary from seconds to minutes as it transfers a plurality of gaseous streams through one or more of the adsorbent bed units.
Rapid cycle swing adsorption processing involves significant footprint or layout area for the valves relative to the available interface cross sectional area of the adsorbent bed. This constraint on the footprint is further complicated by the processing operations, such as dehydration for subsequent cryogenic processes, if pressure drop is to be minimized. Without an optimum arrangement, the required valve footprint may cause the valves to dominate the size of the adsorbent bed units, making the configuration less practical and expensive. Large valves are typically less effective in using the valve footprint (e.g., valve cross-sectional area) because the flow occurs around the periphery of the valve opening for certain types of valves, such as poppet valves. This may result in poor distribution of the flow uniformly across the interface of the adsorbent bed. Also, large poppet valves are limited with respect to the valve opening profile, which limits the flow profiles that can be generated.
To optimize the cycle timing for a swing adsorption process, actively controlled valve actuators are required. The valves have to be forced against seating surfaces to seal properly. At conventional swing adsorption processing pressures, the actuators may involve significant force to open the valve against the pressure and to close the valve against its seat. The necessary mechanism to handle these valve adjustments contributes to bulk (e.g., supporting equipment footprint) and costs in proportion to valve footprint and gas pressure, which is further complicated at higher pressures. For example, the pressure swing process involves changes in pressure between the various steps (e.g., feed or adsorption step and purge step) to move the volume of gas enclosed in the adsorbent bed unit. The differential pressures used for the swing adsorption processes may cause flows for the various steps to reach sonic velocity across the valve seats.
Accordingly, there remains a need in the industry for apparatus, methods, and systems that provided enhancements to the processing of feed streams in gas processing systems. Further, a need exists for a reduction in cost, size, and weight of facilities for treatment of gas streams, which may also minimize problems during pressure swings from valve opening in a swing adsorption process.